The invention relates to a mixer with a conical mixing vat tapering downward toward an outlet and a motor driven mixing worm therein. A mixer of this type is shown in West German PS 2,247,518.
The principle of the known mixer resides in the fact that the mixture components are, in separate mixing ranges, first subject to a coarse mixing and then fed toward a more intensive mixing. The material for mixing, which is fed into the mixer discontinuously, is not directly deposited in the lower mixing range, but only after a phase of preliminary mixing, by which a good mixing result required for a continuous mixture discharge is attained. The separation of the two mixing ranges is achieved by the creation of a conveyance-neutral zone between the conveyance ranges of mixing worms rotating within the mixer housing.
In the outer field of the region affected by the mixing worm's conveyance-neutral zone, the material to be mixed is compressed due to the flow conditions resulting from its various pitches, while in the neighboring range an equilibrium region is created in which an easy passage of one portion of the material to be mixed takes place into the lower mixer range for the purpose of intensive mixing and discharge.
The compression of the materials to be mixed, particularly with the treatment of discontinuously fed mixture components, can have an adverse effect upon those individual mixture components which have a tendency to form agglomerates. Among these could be cited certain organic pigments intended for the coloring of the mixture material.
In certain operational phases, such as at the end of a mixing program, the mixer is only partially filled. Such a partial filling can result in the separation plane of the two mixing regions running diagonally to the mixer axis. The compression zone slopes off so sharply to the equilibrium zone that an adequate separation of the mixing regions is no longer assured.